The first thing you want to do is make sure you're using the correct theme for this achievement. You can change your theme to Cosmos from the main menu.
You can find the Train puzzle in the Hard difficulty section. To unlock the Train puzzle, you must first complete the three puzzles before it.
Completing puzzles is simple in this game (if that's what you want), by abusing the Help (H Key) option. Press H for help, then press the pieces that begin flashing. You can get into a pretty good rhythm of pressing the H key and then clicking on the piece making some of the puzzles (even hard and expert), finish within a minute or two.
Once you unlock the Train puzzle, simply do as I pointed out until it's complete. Once the puzzle is complete, just select New Game and complete the same puzzle four more times.
TIP: If you do happen to fail which is likely you probably will, make sure to select continue. Then undo the last 5-6 moves. Then reshuffle and go back to doing the Help trick. I have never failed a puzzle doing this, but if you do fail again, just Undo further back.